1. Technical Field
The disclosure relates in general to a manufacturing method of a semiconductor device, and more particularly to a manufacturing method of a semiconductor device having an epitaxial structure with a cap layer formed thereon doped with boron.
2. Description of the Related Art
Epitaxial SiGe layers are usually served as a source/drain for semiconductor devices. Since the lattice constant of the epitaxial SiGe layer is larger than that of a silicon substrate, a strain stress generated to the channel region of the semiconductor device, such as a metal-oxide semiconductor (MOS) transistor device, may efficiently improve the device performance.
It is well-known that the strain stress is increased as the Ge concentration in the epitaxial SiGe layer is increased. However, while the increase of the Ge concentration in the epitaxial SiGe layer improves the device performance, it may cause some problems as well. For example, the distinct difference between the Ge concentrations in the SiGe layer and in the adjacent cap layer may cause a strain relaxation to the epitaxial SiGe layer and/or result in a wavy top surface of the structure, rendering undesirable impacts to the subsequent manufacturing processes.